The present invention relates to a process for producing a spherical silica gel.
Spherical silica gels are widely used for a catalyst, a catalyst support, a filler for cosmetics, a medium for column chromatography, a resin filler, an adsorbent or a drying agent, from the viewpoint of varieties in the particle size, the pore structure and the surface physical properties. For such applications, solid particles having no depression or crack on the surface are preferred.
As a process for producing the spherical silica gel, an emulsification method has been known. JP-A-4-154605 discloses a method of emulsifying an aqueous sodium silicate solution or an alkyl silicate in a solvent having no compatibility therewith, followed by gelation with e.g. an acid, an alkali or water. Further, JP-B-4-2525 discloses a method of gelating an aqueous sodium silicate solution or an alkyl silicate with an acid, an alkali or water, followed by emulsification in a solvent having no compatibility therewith, for granulation.
By such emulsification methods, a gel of solid spherical silica particles having no depression can relatively easily be obtained. However, the emulsifying agent to be used is generally expensive, and accordingly the production cost of the spherical silica gel tends to be high.
Further, as a process for producing a spherical silica gel, a spray method also has been widely known. JP-A-61-168520, JP-A-7-138015 and JP-A-7-196310 disclose a method of spray-drying a silica sol to produce a spherical silica gel. JP-A-60-54914, JP-A-60-81012, JPA-3-223107, JP-B-4-68247 and JP-B-5-3413 disclose a method of spray-drying an alkali silica solution for gelation, followed by neutralization to produce a spherical silica gel.
With respect to the spherical silica gel obtainable by such a method, the particles tend to have a pore volume of at most about 0.6 cm3/g in many cases, and it is difficult to control physical properties of the pores. Further, particles having part of their surfaces depressed are likely to form.
The present invention has been made to overcome the above problems, and it is an object of the present invention to provide a process for producing a solid spherical silica gel particles having no depression or crack, having a high particle strength, and having a sharp particle size distribution.
The present invention provides a process for producing a spherical silica gel, which comprises supplying a liquid mixture of an alkali silicate solution and an acid solution to a spraying apparatus, spraying the liquid mixture to obtain droplets, bringing the droplets into contact with a liquid for recovering a silica gel, and recovering the formed spherical silica gel together with the liquid for recovering a silica gel, as a slurry.
Now, the present invention will be described in detail with reference to the preferred embodiments.